1 kW Wind Turbine (12.5 m/s)
2-Blades (Carbon fibre)
1.8 m Diameter
& Induction motor to PMA conversion
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A 1 kW @ 12.5 m/s (2 kW @ 17 m/s) 1.8 metre diameter wind turbine was designed and constructed using carbon fibre composites. The generator was built by converting an induction motor into a permanent magnet generator. Blade power and efficiency have been measured at different tip-speed-ratios and a maximum efficiency of 30% at a TSR of 11.6 was recorded. These results verify the accuracy of calculations from the blade calculator software. Total cost of the generator and blades was less than AU$200.
Keywords: Wind power, Permanent Magnet Generator, Induction motor to PMA conversion, 1kw wind turbine, carbon fibre wind turbine blades
Construction of the Permanent Magnet Generator
The alternators rotor was turned down on a lathe to accommodate neodymium magnets.
The rotor of the alternator was turned (ground away) on a lathe until it fit into the stator with the neodymium magnets attached.
The magnets are placed at an angle to reduce cogging and then fastened in place using a small amount of fibreglass and a layer of carbon fibre.
- Six magnets were carefully placed on a slight angle to reduce cogging of the generator.
- The magnets were fibre glassed in place with two strips of carbon fibre.
Design of a permanent magnet generator was necessary to test and characterise the blade set. Conversion of a 40 amp car alternator to a permanent magnet generator was attempted.
We found this size of neodymium magnet to be too strong for this sized motor. The casing of the alternator was too close to the magnets and required sheilding with sheet metal plate. Too much inductive energy loss was encountered from the changing magnetic field in the aluminium.
Sheet metal was placed inside the stator to shield the magnetic field from aluminium. Without the sheet metal lining, significant power was lost in the aluminium.
The 40 Amp car alternator reassembled after conversion to a permanent magnet generator.
A 1/4 hp induction motor was converted to a permanent magnet generator with much better results.
The generator has zero cogging, this is due to the angled magnets and the 2 mm air gap between the rotor and stator. It is configured for 3 phase, each phase measuring 5.6 ohms. Output voltage is 130 Vrms at 1333 rpm, increasing linearly with rpm.
Given: The 3 phases are isolated and connected as 3 single phase outputs. Each output is rectified to DC using a single phase bridge rectifier.
At 666rpm, generator voltage Vs = 65Volts
Rs = resistance of each phase of the generator (Rs = 5.6 Ohms)
Voltage across Rs = 65 - 48 = 17 Volts
Ploss = V2/R
Power Lost = 172/5.6
Ploss= 51.6 watts per phase
Efficiency of generator = 144/(144+51.6)
Efficiency = 73.6%
V = IR  rearranged to;
V/R = I
Current into battery = 17/5.6
I = 3 amps per phase
(432 watts for all 3 phases)
Power into battery = 48 x 3
P = 144 watts per phase
Calculate power using;     P = VI
The wind turbine blades were designed using the warlock engineering blade calculator program. The airfoil chosen was NACA2412 and a two bladed turbine was designed to have a tip-speed-ratio of 10.
Airfoil cross sectons are cut out of aluminium sheet. They are shown over-layed from smallest to largest in order of their position along the wing.
Wind turbine cross sections aligned and bolted to a frame.
The airfoils cross sections were cut out of 3 mm aluminium sheets. These sheets were bolted to a steel frame, spaced at appropriate distances and aligned.
A negative mould of the airfoil was created by covering the airfoil sections with aluminium tape. A positive mould of the wing is made by fibre glassing the negative mould. The positive moulds are sanded smooth, following the indentations made from the aluminium cross sections.
The gaps between the airfoil sections were filled with aluminium tape and the back of the tape was fibre glassed in place. Wax and mould release was applied to it and two positive moulds were made.
The refined positive moulds are use to make two 'master' negative moulds for blade production.
Two carbon fibre blades were produced from the mould and then joined together using fibreglass mat followed by wrapping with carbon fibre around the join.
The blades were sanded and wrapped in carbon fibre, using an additional layer of carbon fibre around the hub section. The finished blades are extremely light weight.
Careful detailing of the positive mould produced a perfect negative mould. This final negative mould was waxed and mould release was applied. CSM fibreglass (220 g) with vinyl ester resin was applied to each mould. The two mould halves were clamped together after the resin had gelled and the blade was removed after curing.
The moulds were sanded down using the aluminium impressions as a guide. Wax and mould release was applied to the positive moulds and new negative moulds were made out of fibreglass and carbon fibre.
Calculating generator efficiency
Design and construction of the wind turbine blades
500 Watt Kevlar Blades
Continue to summaries about.....
500 W Kevlar Blade Construction
Frequently asked questions about plan orders, blade design, electrical work and generator matching can be found on our Q&A pages.
The same technique was used to convert a larger 1/4 hp induction motor into a 8 pole / 3 phase PMG.
Power output was measured to be more than 2000 watts at the rotational speed for the designed blades. This generator produces enough power for the 1.8 m diameter blades.
Power output was measured to be less than 500 watts at the rpm of the designed blades. The generator will not produce enough power for the 1.8 m diameter blades, it is more suited to 1.0 m diameter blades with a high tip-speed-ratio.
Figure 10. 1.8 m blade set
Figure 9. Negative moulds of the wind turbine blades
Figure 8. Positive moulds of the wind turbine blades
Figure 7. Wind turbine airfoil cross-sections bolted to a frame
Figure 6. Wind turbine airfoil cross-sections
Figure 5. Completed conversion of a 1/4 hp induction motor
Figure 4. Completed conversion of the 40 Amp car alternator
Figure 3. 40 Amp car alternator stator with shielding
Figure 1. 40 Amp car alternator rotor with magnets attached
Figure 2. 40 Amp car alternator rotor with magnets fibre glassed in place